Metal antioxidants for fluid bis (phenoxyphenoxy) benzene



P 3,267,032 lc Patented August 16, 1966 the Navy N Drawing. Filed June27, 1963, Ser. No. 291,216 2 Claims. (Cl. 252-26) The inventiondescribed herein may be manufactured by or for the Government of theUnited States of America for governmental purposes without the paymentofany royalties thereon or therefor.

This invention relates to improvement in the oxidation stability at hightemperatures of a fluid polyphenyl ether which is the meta isomer of his(phenoxyphenoxy) benzene.

Developments in jet engine aircraft have presented an increasing demandfor lubricants which can meet severe operational requirements. Amongsuch requirements is oxidation stability at high temperatures.

The meta isomer of his (phenoxyphenoxy) benzene has heretofore receivedconsiderable attention as a candidate for use as a high temperaturelubricant. It is a liquid having a pour point of 40 F and goodresistance to oxidation, pyrolysis and radiation. The oxidationresistance does not, however, extend to temperatures in the range of 600to 650 F.

It is an object of the present invention to improve the oxidationresistance of the meta isomer of bis (phenoxyphenoxy) benzene attemperatures in the range of 600 to 650 F. whereby to extend the hightemperature range over which this compound may be used as a lubricantand as a hydraulic fluid.

I have found the metals, copper, barium and strontium, to beantioxidants for the meta isomer of bis (phenoxyphenoxy) benzene attemperatures in the range of from about 600 to 650 F. These metals areeffective even in small concentrations, on the order of as low as fromabout 0.050.5% :by weight of the weight of the meta isomer, to impart ahigh degree of oxidation stability to the meta isomer at temperatures inthe aforesaid range.

The metals which are antioxidants in accordance with my invention may bepresent in the meta isomer as such or as a constituent of alloys. Ineither case, the meta isomer will take contact with the metal to receivethe antioxidant protection afforded by the metal. The metals may bebrought into contact with the meta isomer in particle form or in theform of plates or other larger shapes or configurations as foundsuitable. The surface of parts of engines or of other mechanisms withwhich the meta isomer comes into contact, such as oil lines, may consistof the antioxidant metal or a by-pass system may contain the antioxidantmetal in the form of a wire mesh or as a confined mass of granulesthrough which the meta isomer flows in contact before returning to areasof lubrication.

The mechanism whereby the metals function as antioxidants in the metaisomer is not known but is believed to involve formation of metal ionsin the meta isomer.

The oxidation stability imparted to the meta isomer will vary with theparticular metal and will be higher at the lower temperatures in theaforesaid range since the oxidative stress is less at the lowertemperatures.

The antioxidant activity of the metals for the met-a isomer may beevaluated in terms of increase in the viscosity of the meta isomer, thesmaller this increase the greater the oxidation stability imparted tothe meta isomer at a given temperature in the aforesaid range. Acid maybe developed in the meta isomer on heating, but, characteristically,only in small amounts. The neutralization number for this acid may bedetermined but it is of minor and may be of no significance as adetermining factor of the efiicacy of the metals as antioxidants for themeta isomer.

Increase in the viscosity of the meta isomer and the amount of aciddeveloped therein on heating and meta isomer to temperature in theaforesaid range in the presence of the metal antioxidants may bedetermined by use of the dynamic oxidation test procedure and apparatusdescribed in Ind. Eng. Chem., 39, 491 (1947). In this test, equal volumesamples of the meta isomer, with and without a specimen of the metalantioxidant immersed therein, are contained in cyclindrical cells madeof borosilicate glass. The metal specimens, which may be in the form ofstrips, are used in a clean, degreased condition. The sample of the metaisomer without a metal specimen therein is the control. Each of thecells is equipped with a water-cooled condenser fitted to the topthereof and has a rubber tube connected from the condenser to a separatewater trap. Sealed to the upper wall of each of the cells is means fordelivering bubbled air into the bottom of the meta isomer samples in thecells. The cells containing the samples of the meta isomer, with andwithout the metal specimens, are placed in snugly fitting holes in anelectrically heated Duralumen block which is thermostatically controlledto hold at the test temperature i 0.5" F. Clean dry air, free from CO isbubbled through the heated meta isomer samples in the cells at apredetermined volume and rate. The viscosity in centistokes at F. andthe neutralization number of the meta isomer are determined before andafter the test. The neutralization number is the number of milligrams ofpotassium hydroxide required to neutralize the meta isomer.

Indicative of the oxidation stability which can be imparted to the metaisomer by the metal antioxidants of the invention are results obtainedwith commercial meta isomer of bis (phenoxyphenoxy) benzene whichcontained small amounts of adjacently homologous meta polyphenyl ethers.The tests were conducted at temperatures of 600 F. and 650 F. for aperiod of 48 hours, using 20 ml. samples of the commercial meta isomerand metal antioxidant specimens which generally had surface areas of 10square centimeters. The air was bubbled into the meta isomer samples inthe cells at the rate of 1 cc./ gram sample/minute. Test results withthe several metals as antioxidants are set forth in the following table.

DYNAMIC OXIDATION TEST Viscosity Neutraliza- Under the conditions of thetest, the meta isomer which had not been provided with a metalantioxidant, lost all fluidity at 600 F., being oxidized to a gel. Withcopper as the antioxidant, the meta isomer was still fluid at 600 F.,although not at 650 F. Barium and stron- 3 tium as antioxidants provideda greater degree of protection such that the meta isomer was still fluidat 650 F.

Since the invention herein described may be variously embodied withoutdeparting from the spirit or scope thereof, it is intended that thespecific embodiments appearing in the above description shall be takenby way of illustration and not in limitation except as may be defined inthe appended claims.

What is claimed is:

1. A system comprising the meta isomer of bis (phenoxyphenoxy) benzenein contact with an amount of a metal of the group consisting of copper,barium and strontium which is sufiicient to improve the oxidationstability of said meta isomer at a temperature in the range of fromabout 600 to 650 F.

2. A system as defined in claim 1, wherein the metal is strontium.

References Cited by the Examiner UNITED STATES PATENTS 1,992,292 2/1935Cox et al. 260611.5 3,151,082 9/1964 Wesley et al. 2606ll.5

FOREIGN PATENTS 851,651 10/ 1960 Great Britain.

OTHER REFERENCES Ravner et al., Antioxidant Action of Metals andOrganometal Compounds in Fluoresters and Polyphenyl Ethers, NRL Report5794 (Dec. 5, 1962); page 8, most pertinent.

15 DANIEL E. WYMAN, Primary Examiner.

J. R. MCBRIDE, P. P. GARVIN, Assistant Examiners.

1. A SYSTEM COMPRISING THE META ISOMER OF BIS (PHENOXYPHENOXY) BENZENEIN CONTACT WITH AN AMOUNT OF A METAL OF THE GROUP CONSISTING OF COPPER,BARIUM AND STRONTIUM WHICH IS SUFFICIENT TO IMPROVE THE OXIDATIONSTABILITY OF SAID META ISOMER AT A TEMPERATURE IN THE RANGE OF FROMABOUT 600 TO 650*F.